1. Field of the Invention
The present invention relates to the field of data communications networks. More particularly, the present invention relates to an apparatus and method for redirecting network management messages in a cluster of network devices.
2. Background
Two types of data communication networks known to those skilled in the art are Local Area Networks (“LANs”) and Wide Area Networks (“WAN”). Network devices are used to transmit information across networks, which may include various combinations of LANs and WANs. Without limitation, such network devices may include switches, bridges, and routers. “Switching” refers to a technology in which a network device (known as a switch) connects two or more LAN segments. A switch transmits frames of data from one segment to their destinations on the same or other segments. When a switch in an Ethernet LAN begins to operate, it examines the Media Access Control (“MAC”) address embedded in the frames that flow through it to build a table of known sources. If the switch determines that the destination of a frame is on the same segment as the source of the frame, it drops, or filters, the frame because there is no need to transmit it. If the switch determines that the destination is on another segment, it transmits the frame onto the destination segment only. Finally, using a technique known as flooding, if the destination segment is unknown, the switch transmits the frame on all segments except the source segment.
Because a switch maintains a table of the source MAC addresses received on every port, it “learns” to which port a station is attached every time the station transmits. Then, each packet that arrives for that station is forwarded only to the correct port, eliminating the waste of bandwidth on the other ports. Since station addresses are relearned every time a station transmits, if stations are relocated the switch will reconfigure its forwarding table immediately upon receiving a transmission from the stations.
An Ethernet LAN switch improves bandwidth by separating collision domains and selectively forwarding traffic to the appropriate segments. FIG. 1 illustrates the topology of a typical Ethernet network 100 in which a LAN switch 110 has been installed. As shown in FIG. 1, LAN switch 110 has five ports: 120, 130, 140, 150, and 160. The first port 120 is connected to LAN segment 125. The second port 130 is connected to LAN segment 135. The third port 140 is connected to LAN segment 145. The fourth port 150 is connected to LAN segment 155. The fifth port 160 is connected to LAN segment 165. The Ethernet network 100 also includes a plurality of servers 170-A-170-C and a plurality of clients 180-A-180-K, each of which is attached to one of the LAN segments 125, 135, 145, 155, or 165. If server 170-A on port 120 needs to transmit to client 180-D on port 130, the LAN switch 110 forwards Ethernet frames from port 120 to port 130, thus sparing ports 140, 150, and 160 from frames destined for client 180-D. If server 170-C needs to send data to client 180-J at the same time that server 170-A sends data to client 170-D, it can do so because the LAN switch can forward frames from port 140 to port 150 at the same time it is forwarding frames from port 120 to port 130. If server 170-A on port 120 needs to send data to client 180-C, which is also connected to port 120, the LAN switch 110 does not need to forward any frames.
Thus, performance improves in LANs in which LAN switches are installed because the LAN switch creates isolated collision domains. By spreading users over several collision domains, collisions are avoided and performance improves. In addition, many LAN switch installations dedicate certain ports to a single users, giving those users an effective bandwidth of 10 Mbps when using traditional Ethernet. As a LAN grows, either due to additional users or network devices, additional switches must often be added to the LAN and connected together to provide more ports and new network segments.
As LAN and WAN topologies become more complex, network management tools become critically important. As is known to those skilled in the art, the Simple Network Management Protocol (“SNMP”) is one currently popular example of a network management tool. SNMP is a simple request/response protocol that communicates management information between two types of SNMP software entities: SNMP applications (also called SNMP managers) and SNMP agents.
SNMP applications are typically executed in a network management station, and issue queries to gather information about the status, configuration, and performance of external network devices (called network elements in SNMP terminology). The CiscoWorks™ software package, available from Cisco Systems, Inc. of San Jose, Calif., is an example of a network management station, and a LAN switch is an example of a network element that can be managed using SNMP. Relevant details of the SNMP protocol will be discussed in subsequent sections of this document.
Traditionally, network device installation includes inserting the device into the network and assigning it an Internet Protocol (“IP”) address, which is typically a 32-bit number assigned to hosts that want to participate in a TCP/IP Internet. Newer versions of the IP protocol may use more bits for the IP address. The IP address of a network device is a unique address that specifies the logical location of a host or client on the Internet.
Once a network device has been assigned an IP address, a network administrator can enter the device's IP address into a network management station to access the network device and to configure it from anywhere in the Internet using a protocol such as SNMP. However, currently, each network device to be configured and managed must have its own IP address, which must be registered with a domain name service (“DNS”). Assigning an IP address to each and every network device is undesirable, because registering IP addresses with a DNS is both costly and cumbersome.
In order to implement a paradigm where several different devices can be managed and configured as a single network entity (called a “cluster”), what is needed is a way to allow all the device in a cluster to share a single IP address for the purposes of network management. Accordingly, it would be convenient for a network administrator to be able to assign a single IP address to one network device in a cluster, and then to be able to configure and manage all of the network devices in the cluster using this single IP address. Unfortunately, no current mechanism exists to enable this activity. The present invention provides an apparatus and method which permits an entire cluster of network devices to share a single IP address for the purposes of network management, and to provide a commander device which redirects network management data requests and responses (such as SNMP messages) to and from other devices in the cluster. These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and in the associated figures.